A charter bus taking high school students home from a trip to Disney World plunged off a bridge and into a ravine in Alabama early on Tuesday, killing the driver and injuring several others.

The bus was carrying about 50 people when it came off Interstate 10 in Baldwin county, near Mobile. The passengers were members of the band from Channelview high school in the Houston area.

The local sheriff, Hoss Mack, told reporters that one person was in critical condition and five more were seriously injured, while other passengers suffered minor injuries. Some were transported by helicopter to hospitals. Sacred Heart hospital in Pensacola said it took in 18 patients.

Video footage showed a bus with the logo of a Houston-based tour company lying on its side on grassy land next to a creek and embankment with severe damage visible to the front axle and side panels, as first responders with flashlights combed the area. The road was closed in both directions.

Mack said that the accident happened at about 5.30am, when the bus entered the median, then fell about 50ft, forcing rescuers to rappel using ropes to reach the victims. The cause of the incident was not immediately clear.

“This has been an extensive rescue operation,” he said.

John Malone, a state trooper, told a news conference that the driver’s identity had not yet been released pending notification of next of kin. There was “not a whole lot indication that there was braking” before the bus plunged, he said.

“I heard a lot of panicking and screaming, some students were stuck under seats, some were on top of other students, and there was a lot of panic to get people out,” one student told ABC13 local news from a hospital, adding that he felt “one huge bump” and the lights in the bus went out.

On Monday the band had posted a photograph of students at the theme park in Orlando on its Facebook page.